1. Field of the Invention
The present invention relates to an electronically controlled automatic transmission control system.
2. Description of the Prior Art
An electronically controlled automatic transmission control sytem consists of an electronic controller which receives the running conditions, such as the running speed of the vehicle, the degree of throttle opening, the torque of the output shaft and the difference in revolving rate between the input shaft and the output shaft of a fluid coupling, as input signals and provides output signals corresponding to those input signals and a hydraulic controller including a fluid pressure source, hydraulic servomotors adapted to engage, release or fix the components of the gear train (gear type transmission mechanism) to change the reduction ratio, shift control valves for changing over the connection of the fluid pressure source to the hydraulic servomotors, solenoid valves adapted to be controlled by the electronic controller so as to operate the shift control valves by changing the input signal pressures applied to the shift control valves for shift control and a manual selector valve which is movable through predetermined set positions, namely, a neutral position (N-position), a drive position (D-position) and a reverse position (R-position) and adapted to be controlled manually by the driver to change over the connection of the fluid pressure source to the predetermined shift valves or the predetermined hydraulic servomotors.
In a conventional control system of this type, since the shift control valves are not required to be controlled while the manual selector valve is placed at the N-position, no input signal pressure is applied to the shift control valves, whereas an input signal pressure is applied to the shift control valves upon placing the manual selector valve at the D-position. Accordingly, there has been a time lag between the shift of the manual selector valve from the N-position to the D-position for starting the vehicle and the application of an input fluid pressure for controlling the shift control valves, so that the start of the vehicle is delayed. Thus, a vehicle equipped with such a conventional automatic transmission has been accompanied by undesirable driving feeling due to delayed response, which is peculier to a vehicle equipped with an automatic transmission.